The present invention relates to pulsation dampers in general, and especially to a pulsation damper particularly suited for use in a conduit connected to the output of a pump.
It is well known that pressure variations or pulses may occur in a fluid medium being conveyed through pipes or similar conduits, such as discharge conduits connected to and/or communicating with the output ports of reciprocating-type pumps. However, in many cases, it is desired that the fluid be delivered to its ultimate destination at a substantially unvarying pressure at least over the short run, that is, without short-duration pressure excursions, while long-term gradual pressure changes may be acceptable and even desired in some instances.
This situation has already been recognized and attempts have been made to develop pulsation dampers which would damp or suppress the undesired pressure pulses. So, for instance, there are known pulsation dampers containing a constant quantity of enclosed gaseous medium which may be separated from the fluid being conveyed by a movable wall or member which is displaced by the difference between the pressure of the fluid being conveyed and that of the enclosed gaseous medium until equilibrium is achieved. While the pulsation dampers of this type are quite acceptable for many applications, experience has shown that they can work to complete satisfaction only within a rather limited pressure range around the pressure for which they have been originally designed or adjusted, especially if a flexible diaphragm or a bellows is used as the movable wall or member, since otherwise the movable member is subjected to excessive deviations from its original position and thus excessive deformations in the case of use of a flexible diaphragm or bellows as the movable member, with attendant changes in response of the movable member to further pressure changes of the same type as that which has resulted in the excessive displacement or deformation to begin with.
To avoid this disadvantage, it has been proposed in the U.S. Pat. No. 3,741,692, issued June 26, 1973, so to construct the pulsation damper to be used in a discharge conduit from a reciprocatory-type pump and operating on the flexible diaphragm principle as to be able to change the pressure of the enclosed gaseous medium by changing the quantity of such enclosed gaseous medium in dependence on the direction and/or extent of displacement of the movable wall incorporating the flexible diaphragm from its originally selected position. This is achieved by using two separate valves, that is, an inlet valve interposed in a path between a pressurized gaseous medium source and the space containing the enclosed gaseous medium, and an outlet valve arranged in a relief path between such space and the ambient atmosphere. There is further provided an actuating arrangement which is movable in dependence on the movement of the movable wall and thus on the magnitude and direction of the pressure differential between the enclosed gaseous medium and the fluid being conveyed and which opens the inlet valve to admit an additional quantity of the pressurized medium into the aforementioned space when the movable wall is excessively displaced in the direction corresponding to the excess of the pressure of the fluid being conveyed over that of the gaseous medium, or the outlet valve to discharge a quantity of the gaseous medium from such space when the movable wall is excessively displaced in the direction corresponding to the excess of the pressure of the gaseous medium over that of the fluid being conveyed. In this manner, the average pressure of the gaseous medium tracks the average pressure of the fluid being conveyed and the movable wall is moved in a limited range around its desired position irrespective of the absolute values of such average pressures. However, this arrangement is rather complicated, especially because of the provision of the separate inlet and outlet valves and the actuating arrangement therefor which is separate from the movable valve members of such valves, and hence rather expensive. Moreover, because of the separateness of such components, this prior-art arrangement has a high degree of exposure to malfunction since failure of any of the valves to follow the movement of the actuating arrangement when such movement is called for will render the entire pulsation damper inoperative for the desired purpose even though the actuating arrangement and the respectively other valve are still capable of operating properly.